Light emitting diode with high illumination

ABSTRACT

A light emitting diode ( 80 ) includes a first and a second semiconductor structures ( 30, 40 ), and an adhesive layer ( 34, 46 ) between the first and the second semiconductor structures. The first semiconductor structure includes a n-type AlGaInP cladding layer ( 13 ), a p-type AlGaInP cladding layer ( 17 ), an AlGaInP active layer ( 15 ) between the n-type and the p-type AlGaInP cladding layers, a transparent conducting layer ( 62 ) on the n-type AlGaInP cladding layer, a first electrical contact ( 82 ) on the transparent conducting layer, ohmic electrodes ( 21 ) ohmic contact the p-type AlGaInP cladding layer, and a reflecting layer ( 32 ) on an opposite side of the p-type AlGaInP cladding layer to the AlGaInP active layer. The second semiconductor structure includes a carrier substrate ( 42 ), an ohmic contact layer ( 44 ) on the carrier substrate, and a second electrical contact ( 74 ) on an opposite side of the carrier substrate to the ohmic contact layer.

BACKGROUND

1. Technical Field

The present invention generally relates to structures of light emittingdiodes.

2. Description of Related Art

Light emitting diodes (LEDs) are a type of semiconductor light sourcethat are widely used in electrical products such as scientificinstruments, medical instruments, or electronic consumer products, dueto their high brightness, long life-span, and wide color gamut. However,the electrical resistivity of a p-type cladding layer of LEDs iscomparatively high, resulting in electric current supplied to the LEDsnot being uniformly distributed over the p-type cladding layer in alateral direction and flowing toward an active light emitting layerlocated below the p-type cladding layer. This is often referred to ascurrent crowding. Current crowding induces light emitted from differentareas of the LED having different illuminations which decreases lightemitting efficiency of the LED.

Referring to U.S. Pat. No. 5,869,849, a LED which has decreased currentcrowding problem is provided. The light-emitting diode is provided bysuch steps: i) forming a double hetero-structure of AlGaInP, whichincludes a p-type AlGaInP cladding layer, an active AlGaInP layer and an-type AlGaInP cladding layer, on a GaAs substrate; ii) bonding a n-typeGaP layer to the double hetero-structure of AlGaInP by wafer bondingtechnique, and removing the GaAs substrate from the doublehetero-structure of AlGaInP; (iii) sequentially forming a p-type GaAsohmic contact layer and an indium tin oxide (ITO) current spreadinglayer on the p-type AlGaInP cladding layer; iv) respectively forming afirst electrical contact on the n-type GaP layer and a second electricalcontact on the indium tin oxide current spreading layer.

In the forgoing LED of U.S. Pat. No. 5,869,849, the GaAs substrate,which is an opacity substrate, is replaced by the n-type GaP layer whichsevers as a transparent window layer of the LED and the light generatedby the double hetero-structure of AlGaInP is emitted via the windowlayer. The n-type GaP layer has good electrical conductivity whichdecreases current crowding of the LED, and the electric current isdispersed by the indium tin oxide current spreading layer which furtherdecreases current crowding of the LED.

However, in the forgoing LED of U.S. Pat. No. 5,869,849, the GaP layerand the double hetero-structure of AlGaInP are bonded together bydirectly pressing the GaP layer toward the double hetero-structure ofAlGaInP, which causes a bonding force generated between the GaP layerand the double hetero-structure of AlGaInP not adequate enough tofixedly bond the n-type GaP layer with the double hetero-structure ofAlGaInP. Therefore, the n-type GaP layer and the double hetero-structureof AlGaInP need to be heated to 650° C. for 30 minutes in the oven so asto fixedly bond the n-type GaP layer with the double hetero-structure ofAlGaInP. This will harmfully affect the double hetero-structure ofAlGaInP and decreases qualified rate of the LED.

What is needed, therefore, is a LED which needs not to be heated duringmanufacturing process and has a high qualifying rate.

SUMMARY

The present invention provides a light emitting diode with highillumination. The light emitting diode includes a first semiconductorstructure, a second semiconductor structure and an adhesive layer. Thefirst semiconductor structure includes a n-type AlGaInP cladding layer,a p-type AlGaInP cladding layer, an AlGaInP active layer sandwichedbetween the n-type AlGaInP cladding layer and the p-type AlGaInPcladding layer, a transparent conducting layer on the n-type AlGaInPcladding layer, a first electrical contact on the transparent conductinglayer, a plurality of ohmic electrodes in ohmic contact with the p-typeAlGaInP cladding layer, and a reflecting layer formed on an oppositeside of the p-type AlGaInP cladding layer to the AlGaInP active layer.The second semiconductor structure includes a carrier substrate, anohmic contact layer formed on the carrier substrate, and a secondelectrical contact formed on an opposite side of the carrier substrateto the ohmic contact layer. The adhesive layer is sandwiched between thereflecting layer of the first semiconductor structure and the ohmiccontact layer of the second semiconductor structure.

Other advantages and novel features of the present light emitting diodewill become more apparent from the following detailed description ofpreferred embodiments when taken in conjunction with the accompanyingdrawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an epitaxy structure of a light emitting diode according toa first embodiment of the present invention, the epitaxy structureincludes a n-type GaAs substrate, an n-type AlGaInP cladding layerlocated on the GaAs substrate, an AlGaInP active layer located on then-type AlGaInP cladding layer, and a p-type AlGaInP cladding layerlocated on the AlGaInP active layer.

FIG. 2 shows a structure obtained during manufacturing the present lightemitting diode, the structure is obtained from forming a plurality ofpoint-like ohmic electrodes on the p-type AlGaInP cladding layer of theepitaxy structure of FIG. 1.

FIG. 3 shows a first semiconductor structure which is obtained fromspreading a metallic reflecting layer on the p-type AlGaInP claddinglayer of the epitaxy structure and the point-like ohmic electrodes, andspreading a first adhesive layer on the metallic reflecting layer.

FIG. 4 shows a second semiconductor structure which includes a carriersubstrate, an ohmic contact layer on the carrier substrate, and a secondadhesive layer on the ohmic contact layer.

FIG. 5 shows a light-emitting diode chip which is obtained from bondingthe first and the second semiconductor structures together and removingthe GaAs substrate from the first semiconductor structure.

FIG. 6 shows a structure obtained during manufacturing the present lightemitting diode, the structure is obtained from forming a transparentconducting layer on the n-type AlGaInP cladding layer of thelight-emitting diode chip of FIG. 5.

FIG. 7 shows the light emitting diode according to the first embodimentof the present invention, the light emitting diode is obtained fromforming a first electrical contact on the transparent conducting layerand forming a second electrical contact on a bottom surface of thecarrier substrate.

FIG. 8 is a transverse sectional view of a light emitting diodeaccording to a second embodiment of the present invention.

FIG. 9 is a top view of the light emitting diode of FIG. 8.

FIG. 10 is a top view of a light emitting diode according to a thirdembodiment of the present invention.

FIG. 11 is a transverse sectional view of a light emitting diodeaccording to a fourth embodiment of the present invention.

FIG. 12 is a transverse sectional view of an epitaxy structure of alight emitting diode according to a fifth embodiment of the presentinvention.

FIG. 13 is a transverse sectional view of the light emitting diodeaccording to the fifth embodiment of the present invention.

DETAILED DESCRIPTION

Reference will now be made to the drawing figures to describe thepreferred embodiment in detail.

The present invention provides a light emitting diode 70 (shown in FIG.7). Referring to FIGS. 1 to 7, the light emitting diode 70 ismanufactured by the following steps:

Referring to FIG. 1, an epitaxy structure 10 is shown. The epitaxystructure 10 includes an n-type gallium arsenide (GaAs) substrate 14 anda semiconductor light-emitting structure 12 located on top of the GaAssubstrate 14. The semiconductor light-emitting structure 12 is a doublehetero-structure of AlGaInP which includes a n-type aluminum indiumgallium phosphide (AlGaInP) cladding layer 13 located on top of the GaAssubstrate 14, an AlGaInP active layer 15 located on top of the n-typeAlGaInP cladding layer 13, and a p-type AlGaInP cladding layer 17located on top of the AlGaInP active layer 15.

Referring to FIG. 2, a plurality of point-like ohmic electrodes 21 arepartially formed on the p-type AlGaInP cladding layer 17 of the epitaxystructure 10. The point-like ohmic electrodes 21 are formed on theepitaxy structure 10 sequentially by mesa etching, metallizing, andthermal treatment processes. The point-like ohmic electrodes 21 arediscretely distributed on the p-type AlGaInP cladding layer 17 of theepitaxy structure 10, guiding electric current to uniformly distributeover the epitaxy structure 10.

Referring to FIG. 3, a metallic reflecting layer 32 and a first adhesivelayer 34 are sequentially spread on the epitaxy structure 10, and afirst semiconductor structure 30 is obtained. The metallic reflectinglayer 32 is spread on and contacts with the p-type AlGaInP claddinglayer 17 of the epitaxy structure 10. The first adhesive layer 34 isspread on and contacts with the metallic reflecting layer 32. Themetallic reflecting layer 32 fills spaces between and around thepoint-like ohmic electrodes 21. The metallic reflecting layer 32includes metal with high reflectivity, such as aluminum, silver, or etc.The first adhesive layer 34 is preferably selected from a groupconsisting of silver (Ag), gold (Au), tin (Sn), gold tin (AuSn), plumbumtin (PbSn), indium (In), indium palladium (InPd), indium tin oxide(ITO).

Referring to FIG. 4, a second semiconductor structure 40 is provided.The second semiconductor structure 40 includes a carrier substrate 42,an ohmic contact layer 44 formed on the carrier substrate 42, and asecond adhesive layer 46 formed on the ohmic contact layer 44.Optimally, a material of the carrier substrate 42 is selected fromsilicon (Si), silicon carbide (SiC), and a group III-V compoundmaterial.

Referring to FIG. 5, the first semiconductor structure 30 is bonded tothe second semiconductor structure 40, and the GaAs substrate 14 isremoved from the first semiconductor structure 30, and a light-emittingdiode chip 50 is obtained. The first semiconductor structure 30 isbonded to the second semiconductor structure 40 via wafer bondingtechnique. The GaAs substrate 14 is removed from the first semiconductorstructure 30 via grinding or selective etching method.

Referring to FIG. 6, a transparent conducting layer 62 is formed on then-type AlGaInP cladding layer 13 of the light-emitting diode chip 50.Preferably, the transparent conducting layer 62 ohmic contacts with then-type AlGaInP cladding layer 13 of the light-emitting diode chip 50. Amaterial of the transparent conducting layer 62 can be selected from tinprotoxide (SnO), indium-doped tin oxide (SnO:In), antimony-doped tindioxide (SnO₂:Sb), zinc-doped indium oxide (In₂O₃:Zn), tin-doped indiumsilver oxide (AgInO₂:Sn), indium tin oxide (ITO), zinc oxide (ZnO),aluminum-doped zinc oxide (ZnO:Al), zinc gallium oxide (ZnGa₂O₄),tin-doped gallium oxide (Ga₂O₃:Sn), etc.

Referring to FIG. 7, a first electrical contact 72 is formed on thetransparent conducting layer 62, and a second electrical contact 74 isformed on a bottom surface of the carrier substrate 42. Accordingly, thelight emitting diode 70 is obtained.

In the present light emitting diode 70, the first and the secondsemiconductor structures 30, 40 are bonded together by bonding forcegenerated between the first adhesive layer 34 of the first semiconductorstructure 30 and the second adhesive layer 46 of the secondsemiconductor structure 40. Therefore, there in no need to co-heat thefirst and the second semiconductor structures 30, 40 in a hightemperature for a long time for bonding the first and the secondsemiconductor structures 30, 40 together. Thus, the present lightemitting diode 70 has better light emitting capability and higherqualifying rate than the related LED of U.S. Pat. No. 5,869,849.Moreover, the transparent conducting layer 62 ohmic contacts with then-type AlGaInP cladding layer 13 of the light emitting diode 70.Therefore, there is no need for an additional secondary epitaxial growthstep in the manufacturing of the present light emitting diode 70 and themanufacturing process of the present light emitting diode 70 issimplified and the manufacturing cost of the present light emittingdiode 70 is decreased.

In the manufacturing process of the present light emitting diode 70, themetallic reflecting layer 32 shown in FIG. 3 can be omitted, whichallows the ohmic electrodes 21 to directly contact with the firstadhesive layer 34. The transparent conducting layer 62 shown in FIG. 7can also be omitted and the first electrical contact 72 is directlyformed on the n-type AlGaInP cladding layer 13.

Referring to FIGS. 8 and 9, a second embodiment of the present lightemitting diode 80 is shown. In the second embodiment, a round receivinghole 81 is etched through the transparent conducting layer 62 and afirst electrical contact 82 is formed in the receiving hole 81 of thetransparent conducting layer 62. The first electrical contact 82 has atop end extending upwardly above a top surface of the transparentconducting layer 62, and a bottom end contacting with a top surface ofthe n-type AlGaInP cladding layer 13. In the second embodiment, thefirst electrical contact 82 is formed in the receiving hole 81 of thetransparent conducting layer 62 which induces the first electricalcontact 82 to intimately contact with the transparent conducting layer62.

Referring to FIG. 10, a third embodiment of the present light emittingdiode 85 is shown. In the third embodiment, configurations of thereceiving hole 84 and the first electrical contact 83 are different fromconfigurations of the receiving hole 81 and the first electrical contact82 of the second embodiment. In the third embodiment, the receiving hole84 includes a round center portion 84 a and a plurality of fingerportions 84 b radially extending outwardly from the round center portion84 a. Therefore, the first electrical contact 83 includes a plurality offinger portions extending outwardly toward an outer edge of thetransparent conducting layer 62. Thus, electric current can be dispersedover the light emitting diode 85 via the finger portions of the firstelectrical contact 83.

Referring to FIG. 11, a fourth embodiment of the present light emittingdiode 92 is shown. In the fourth embodiment, the carrier substrate 42 isdifferent from the carrier substrate 42 of the first embodiment. Thecarrier substrate 42 of the fourth embodiment is made of ceramicmaterial which has a good thermal conductivity. A plurality of throughholes 91 are defined in the carrier substrate 42 for fillingelectrically conductive material therein. Electric current can flowthrough the carrier substrate 42 through the electrically conductivematerial. Therefore, the ceramic carrier substrate 42 induces thepresent light emitting diode 92 has good heat dissipation capability.

Referring to FIGS. 12 and 13, a fifth embodiment of the present lightemitting diode 90 is shown. The difference between the fifth embodimentand the first embodiment is: a Bragg reflecting layer 23 is spread onthe epitaxy structure 10 of FIG. 1, and a plurality of receivingapertures are etched through the Bragg reflecting layer for forming thepoint-like ohmic electrodes 21 therein. The first adhesive layer 34 isthen formed on the Bragg reflecting layer 23 and the light emittingdiode 90 of the fifth embodiment is manufactured according to the stepsshown in the first embodiment. The Bragg reflecting layer 23 of thefifth embodiment has better reflectivity than the metallic reflectinglayer 32 of the first embodiment. Therefore, the light emitting diode 90of the fifth embodiment has better reflectivity than the light emittingdiode 70 of the first embodiment.

It is to be understood, how ever, that even though numerouscharacteristics and advantages of the present invention have been setforth in the foregoing description, together with details of thestructure and function of the invention, the disclosure is illustrativeonly, and changes may be made in detail, especially in matters of shape,size, and arrangement of parts within the principles of the invention tothe full extent indicated by the broad general meaning of the terms inwhich the appended claims are expressed.

1. A light emitting diode comprising: a first semiconductor structurecomprising: a double hetero-structure comprising a n-type AlGaInPcladding layer, a p-type AlGaInP cladding layer, and an AlGaInP activelayer sandwiched between the n-type AlGaInP cladding layer and thep-type AlGaInP cladding layer; a transparent conducting layer on then-type AlGaInP cladding layer; a first electrical contact on thetransparent conducting layer; a plurality of ohmic electrodes in ohmiccontact with the p-type AlGaInP cladding layer; and a reflecting layerformed on an opposite side of the p-type AlGaInP cladding layer to theAlGaInP active layer; a second semiconductor structure comprising: acarrier substrate; an ohmic contact layer formed on the carriersubstrate; and a second electrical contact formed on an opposite side ofthe carrier substrate to the ohmic contact layer; and an adhesive layersandwiched between the reflecting layer of the first semiconductorstructure and the ohmic contact layer of the second semiconductorstructure.
 2. The light emitting diode of claim 1, further comprising atransparent conducting layer formed on and in ohmic contact with then-type AlGaInP cladding layer.
 3. The light emitting diode of claim 2,wherein the transparent conducting layer defines a receiving holetherethrough, the first electrical contact extending through thereceiving hole of the transparent conducting layer and in contact withthe n-type AlGaInP cladding layer.
 4. The light emitting diode of claim3, wherein the receiving hole comprises a center portion and a pluralityof finger portions radially and outwardly extending from the centerportion.
 5. The light emitting diode of claim 2, wherein a material ofthe transparent conducting layer is selected from the group consistingof tin protoxide, indium-doped tin oxide, antimony-doped tin dioxide,zinc-doped indium oxide, tin-doped indium silver oxide, indium tinoxide, zinc oxide, aluminum-doped zinc oxide, zinc gallium oxide, andtin-doped gallium oxide.
 6. The light emitting diode of claim 1, whereinthe reflecting layer is a metallic reflecting layer which embeds theohmic electrodes therein.
 7. The light emitting diode of claim 1,wherein the reflecting layer is a Bragg reflecting layer which defines aplurality of receiving apertures therethrough receiving the ohmicelectrodes therein.
 8. The light emitting diode of claim 1, wherein theadhesive layer is comprised of a material selected from the groupconsisting of silver, gold, tin, gold tin, plumbum tin, indium, indiumpalladium, and indium tin oxide.
 9. The light emitting diode of claim 1,wherein a material of the carrier substrate is selected from the groupconsisting of silicon, silicon carbide, and III-V compound material. 10.The light emitting diode of claim 1, wherein the carrier substrate ismade of ceramic material, a plurality of through holes being defined inthe substrate with electrically conductive material filled therein.